Stack...
...or not, it would be HUGE if Dell would standardize its storage software stack across EQL and Compellent especially if they would maintain external/third-party storage support.
Commvault acquisition sounds great except they have gazillion partnerships - haven't they just announced some 400th agreement yesterday? - and becoming part of Dell could break all hell loose in the reseller chain...
Dell would be better off buying a real (fully vertical) networking company because their current portfolio is all over the place eg mash of Dell, Brocade and Juniper units - Juniper would be a nice catch but over $20B it's pricey as hell
By now Dell picked up EqualLogic, Ocarina, Exanet and Compellent and while CVLT could fit there it's not essential by any means; they rather need to get busy whipping all these IPs into one scalable stack now, I think.